The present invention is directed to improved casing tongs which are adapted to be suspended from a top head drive assembly in an earth drilling machine and can be used to grip and rotate casing.
Earth-drilling machines are used to make up a large number of threaded connections in the assembly of strings of casing and other down hole tubulars. Various types of tools have been used for this purpose in the past, including tools mounted to move with a top head drive assembly and tools mounted to remain on the floor of the drilling machine.
Tools of the first type are shown in U.S. Pat. Nos. 4,511,169, 4,522,439, and 4,650,236, all assigned to the assignee of the present invention. Each of these devices is adapted to be threaded to a quill included in the top head drive assembly for rotation by the quill, and each includes means for engaging the upper end of a length of downhole tubular. The devices shown in these patent documents include movable jaws which are primarily adapted for lifting and supporting the downhole tubular. These tools are limited in the maximum torque that can be transmitted to the tubular.
The tools shown in U.S. Pat. Nos. 4,650,236 and 4,762,187 (also assigned to the assignee of this invention) include a seal for plugging and sealing the upper end of the tubular, and a passageway for introducing drilling fluid into the tubular. These features provide important blowout protection, as explained in detail in the specifications.
The devices described above provide important advantages in operation. Nevertheless, none of these devices uses cammed jaws operating on the exterior surface of the downhole tubular as described below, and such an arrangement provides particular advantages for casing tongs.
Cammed jaws have been used in a variety of other applications. For example, Wilms U.S. Pat. Nos. 3,793,913, Dickmann 3,550,485, and Peck 4,357,843 all relate to power tongs for an earth-drilling apparatus. In each case, the power tongs are intended to be located on the drilling floor, and they are moved into and out of alignment with the drill string as necessary. Wilms discloses a three-lobed, bidirectional cam which advances and retracts three jaws into engagement with a downhole tubular. A shown in FIG. 2 of the Wilms patent, this device is typically used with the lower rather than the upper end of the tubular. Disc brakes are positioned within the device to advance the jaws into contact with the tubular, and hydraulic motors and cylinders are used to rotate the clamped tubular. The Dickmann and Peck devices are in many respects similar to the Wilms device.
Each of these three power tongs is a heavy, large, complicated and expensive apparatus that takes up considerable space on the drilling floor, and which requires a prime mover which is separate from the prime mover used to rotate the drill string during drilling operations. Because these power tongs are situated on the drilling floor, they must be aligned properly with the drilling axis. Furthermore, they cannot provide blowout protection because they are not in communication with the interior of the clamped tubular. This is a direct consequence of the fact that these tongs work with the lower rather than the upper end of the clamped tubular.
Cam-driven jaws have also been used with hydraulic actuated slip assemblies (Cox U.S. Pat. No. 4,576,254) and with various chucks for pipes and the like, as shown in the following patents:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 3,610,640 Bollin et al 2,016,652 Poole 1,740,377 Snyder 1,292,747 Foster 1,200,612 Helm ______________________________________
None of the patents and patent applications described above provides the important advantages of cam-operated jaws operating on the exterior surface of a casing in an apparatus mountable to a top head drive assembly.